Support latest firebase_storage version

[percula]

:sparkles: What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Chore

:arrow_heading_down: What is the current behavior?

Support for firebase_storage 3.x and 4.x

:new: What is the new behavior (if this is a feature change)?

Support for firebase_storage 3.x through 5.x

:boom: Does this PR introduce a breaking change?

No

:bug: Recommendations for testing

I've tested this against the latest version and it works. The latest firebase_storage renamed some methods but none of the renamed methods are used in this package.

:memo: Links to relevant issues/docs

https://github.com/FirebaseExtended/flutterfire#firebase_remote_config

:thinking: Checklist before submitting

• [x] All projects build
• [x] Follows style guide lines (code style guide)
• [x] Relevant documentation was updated
• [x] Rebased onto current develop

[percula]

This PR also changes the flutter_cache_manager dependency to the stable version 2.0.0.

[renefloor]

Merged #254 instead of this